The purpose of the proposed research is to develop methods by which the neural correlates of important social developments late in the first year of life can be assessed. Between 6 and 12 months of age, infants develop behavioral strategies that are important for later social functioning. For example, infants form long-lasting attachment bonds that may have an impact on the way they view relationships throughout life. It is during this interval that infants also show the rudimentary beginnings of understanding of others. Infants begin to use the facial expressions and vocalizations of familiar adults to regulate their emotions and behavior through social referencing. These behaviors are likely to be important for normal social function, and are severely impaired in children with developmental disorders such as autism. Despite our relatively comprehensive understanding of the behavioral developments in these areas, little is known about the developments in brain systems that allow them to occur. A major motivation in this research plan is the importance of examining both brain and behavior in the context of one another. In other words, it is not enough to examine only brain, or only behavior. Rather we are motivated by the need to examine them in concert. In the proposed studies, we will measure behavioral correlates of social referencing and attachment behavior. To measure the neural correlates of social referencing, we will measure infants' brain activity in response to objects for which primary caregivers have provided positive or negative referencing information. To understand brain developmental changes in attachment, we will measure brain activity in response to the mother's face and a stranger's face. In both cases, we will relate neural responses to environmental factors that are thought to influence social development. There are three major goals in this study. First, we seek to understand the development of brain systems that underlie aspects of social development in humans. Second, we will describe how these brain systems are modified by differences in the childrearing environment. Finally, we will relate the neural correlates of different domains within social development to one another to describe similarities and differences in brain systems that underlie specific behavior.